Approximately 40 human chemokines have been described, that function, at least in part, by modulating a complex and overlapping set of biological activities important for the movement of lymphoid cells and extravasation and tissue infiltration of leukocytes in response to inciting agents (See, for example: P. Ponath, Exp. Opin. Invest. Drugs, 7:1-18, 1998). These chemotactic cytokines, or chemokines, constitute a family of proteins, approximately 8-10 kDa in size. Chemokines appear to share a common structural motif, that consists of 4 conserved cysteines involved in maintaining tertiary structure. There are two major subfamilies of chemokines: the “CC” or β-chemokines and the “CXC” or α-chemokines. The receptors of these chemokines are classified based upon the chemokine that constitutes the receptor's natural ligand. Receptors of the β-chemokines are designated “CCR”; while those of the α-chemokines are designated “CXCR”.
Chemokines are considered to be principal mediators in the initiation and maintenance of inflammation. More specifically, chemokines have been found to play an important role in the regulation of endothelial cell function, including proliferation, migration and differentiation during angiogenesis and re-endothelialization after injury (Gupta et al., J. Biol. Chem., 7:4282-4287, 1998). Two specific chemokines have been implicated in the etiology of infection by human immunodeficiency virus (HIV).
In most instances, HIV initially binds via its gp120 envelope protein to the CD4 receptor of the target cell. A conformational change appears to take place in the gp120 which results in its subsequent binding to a chemokine receptor, such as CCR-5 (Wyatt et al., Science, 280:1884-1888 (1998)). HIV-1 isolates arising subsequently in the infection bind to the CXCR-4 chemokine receptor. In view of the fact that the feline immunodeficiency virus, another related retrovirus, binds to a chemokine receptor without needing to bind first to the CD4 receptor, suggests that chemokine receptors may be the primordial obligate receptors for immunodeficiency retroviruses (Richardson et al., J. Virol. 73:661 (1999)).
Following the initial binding by HIV to CD4, virus-cell fusion results, which is mediated by members of the chemokine receptor family, with different members serving as fusion cofactors for macrophage-tropic (M-tropic) and T cell line-tropic (T-tropic) isolates of HIV-1 (Carroll et al., Science, 276: 273-276 1997). During the course of infection within a patient, it appears that a majority of HIV particles shift from the M-tropic to the more aggressive T-tropic viral phenotype (Miedema et al., Immune. Rev., 140:35 (1994)). Curiously, the M-tropic viral phenotype correlates with the virus's ability to enter the cell following binding of the CCR-5 receptor, while the T-tropic viral phenotype correlates with viral entry into the cell following binding and membrane fusion with the CXCR-4 receptor. Clinically observations suggest that patients who possess genetic mutations in the CCR-5 appear resistant or less susceptible to HIV infection.
However, the binding of chemokine receptors to their natural ligands appears to serve a more evolutionary and central role than only as mediators of HIV infection (Chemokines In Diseaes: Biology And Clinical Research; ed. Caroline A. Hebert 1999). The chemokine receptor, CXCR-4 has been found to be essential for the vascularization of the gastrointestinal tract (Tachibana et al., Nature, 393:591-594 (1998)) as well as haematopoiesis and cerebellar development (Zou et al., Nature, 393:591-594 (1998)). Interference with any of these important functions served by the binding of pre-B-cell growth-stimulating factor/stromal derived factor (PBSF/SDF-1) to the CXCR-4 chemokine receptor results in lethal deficiencies in vascular development, haematopoiesis and cardiogenesis. Similarly, fetal cerebellar development appears to rely upon the effective functioning of CXCR-4 in neuronal cell migration and patterning in the central nervous system. This G-protein-coupled chemokine receptor appears to play a critical role in ensuring the necessary patterns of migration of granule cells in the cerebellar anlage. Interactions of SDF-1 and CXCR4 are also important in maintaining B-cell lineage and in retaining stem cells in bone marrow (Peled et al., Science 283: 845 (1999); Springer et al., Immunity 10:463 (1999)).
In attempting to better understand the relationship between chemokines and their receptors, recent experiments to block the binding of HIV to the CXCR-4 chemokine receptor were carried out through the use of monoclonal antibodies or small molecules that appear to suggest a useful therapeutic strategy (Schols et al., J. Exp. Med. 186:1383-1388 (1997); Schols et al., Antiviral Research 35:147-156 (1997)). Small molecules, such as bicyclams, appear to specifically interfere with the CXCR-4 binding and not CCR-5 binding (Donzella et al., Nature Medicine, 4:72-77 (1998)). These experiments demonstrated interference with HIV entry and membrane fusion into the target cell in vitro. Additional experiments monitoring the calcium flux or Ca2+ mobilization assay demonstrated that a bicyclam also functioned as an antagonist to signal transduction resulting from the binding of stromal derived factor or SDF-1α, the natural chemokine to CXCR-4.
Further, the etiology or association of chemokine receptor binding in the proliferation of glioblastoma tumor cells has been reported by Sehgal et al., J. of Surg. Oncolo. 69:99-104 (1998) (“Sehgal I”) and Sehgal et al., J. of Surg. Oncolo. 69:239-248 (1998) (“Sehgal II”). The role of CXCR4 of its binding to its receptor appears to play a significant role in the formation and/or proliferation of glioblastoma cells. The inhibition of the binding by CXCR4 to its natural receptor ligand by compounds of the present invention, such as AMD 3100, offer a new drug in the treatment tumors of central nervous system that are mediated or associated with chemokines, such as CXCR4.
Additionally, CXC chemokines have been found to regulate or are associated with the regulation of angiogenesis in non-small cell lung cancer (see: Arenberg, et al., J. of Leukocyte Biol.; 62:554562 (1997); and Moore et al. TCM, vol 8(2): 51-58 (1998) Elsevier Science, Inc.). The role of CXC chemokines and the binding to their respective receptors appear to play a significant role in the formation and/or proliferation of non-small cell lung cancer. The inhibition of the binding of these CXC chemokines to their natural receptor ligands by compounds of the present invention, such as AMD 3100, offer a new drug in the treatment tumors such as non-small cell lung cancer that are mediated or associated with increased levels of chemokines.
U.S. Pat. No. 5,583,131, U.S. Pat. No. 5,698,546 and U.S. Pat. No. 5,817,807 disclose cyclic compounds that are active against HIV-1 and HIV-2 in in vitro tests. We have now discovered that these compounds exhibit anti-HIV (anti-human immunodeficiency virus) and anti-FIV (anti-feline immunodeficiency virus) activities due to their binding to the chemokine receptor 4 (CXCR-4 or Fusin receptor), expressed on the surface of certain cells of the immune system (Este et al., Mol. Pharmacol. 55:67 (1999); Egberink et al., J. Virol. 73:6346-6352 (1999)). This competitive binding thereby protects these target cells from infection by HIV which utilize the CXCR-4 receptor for entry. We have discovered that the disclosed compounds also antagonize the binding, signaling and chemotactic effects of the natural CXC-chemokine for CXCR-4, stromal cell-derived factor 1α (SDF-1α). Herein, we further disclose novel compounds that demonstrate protective effects against HIV infection of target cells by inhibition of binding in vitro to the CC-5 receptor (CCR-5).